/*
 * Copyright (C) 2009 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.io.Serializable;
import java.util.Collection;
import java.util.EnumSet;
import java.util.Set;

import com.google.common.annotations.GwtCompatible;

/**
 * Implementation of {@link ImmutableSet} backed by a non-empty
 * {@link java.util.EnumSet}.
 * 
 * @author Jared Levy
 */
@GwtCompatible(serializable = true)
@SuppressWarnings("serial")
// we're overriding default serialization
final class ImmutableEnumSet<E /* extends Enum<E> */> extends ImmutableSet<E> {
    /*
     * Notes on EnumSet and <E extends Enum<E>>:
     * 
     * This class isn't an arbitrary ForwardingImmutableSet because we need to
     * know that calling {@code clone()} during deserialization will return an
     * object that no one else has a reference to, allowing us to guarantee
     * immutability. Hence, we support only {@link EnumSet}.
     * 
     * GWT complicates matters. If we declare the class's type parameter as <E
     * extends Enum<E>> (as is necessary to declare a field of type EnumSet<E>),
     * GWT generates serializers for every available enum. This increases the
     * size of some applications' JavaScript by over 10%. To avoid this, we
     * declare the type parameter as just <E> and the field as just Set<E>.
     * writeReplace() must then use an unchecked cast to return to EnumSet,
     * guaranteeing immutability as described above.
     */
    private final transient Set<E> delegate;

    ImmutableEnumSet(Set<E> delegate) {
        this.delegate = delegate;
    }

    @Override
    public UnmodifiableIterator<E> iterator() {
        return Iterators.unmodifiableIterator(delegate.iterator());
    }

    public int size() {
        return delegate.size();
    }

    @Override
    public boolean contains(Object object) {
        return delegate.contains(object);
    }

    @Override
    public boolean containsAll(Collection<?> collection) {
        return delegate.containsAll(collection);
    }

    @Override
    public boolean isEmpty() {
        return delegate.isEmpty();
    }

    @Override
    public Object[] toArray() {
        return delegate.toArray();
    }

    @Override
    public <T> T[] toArray(T[] array) {
        return delegate.toArray(array);
    }

    @Override
    public boolean equals(Object object) {
        return object == this || delegate.equals(object);
    }

    private transient int hashCode;

    @Override
    public int hashCode() {
        int result = hashCode;
        return (result == 0) ? hashCode = delegate.hashCode() : result;
    }

    @Override
    public String toString() {
        return delegate.toString();
    }

    // All callers of the constructor are restricted to <E extends Enum<E>>.
    @SuppressWarnings({ "unchecked", "rawtypes" })
    @Override
    Object writeReplace() {
        return new EnumSerializedForm((EnumSet) delegate);
    }

    /*
     * This class is used to serialize ImmutableEnumSet instances.
     */
    private static class EnumSerializedForm<E extends Enum<E>> implements
            Serializable {
        final EnumSet<E> delegate;

        EnumSerializedForm(EnumSet<E> delegate) {
            this.delegate = delegate;
        }

        Object readResolve() {
            // EJ2 #76: Write readObject() methods defensively.
            return new ImmutableEnumSet<E>(delegate.clone());
        }

        private static final long serialVersionUID = 0;
    }
}
